System for controlling atmosphere gas inside furnace

ABSTRACT

A system for controlling atmospheric gas inside a furnace may include a furnace into which an atmospheric gas is charged for thermaltreating carbon steel, a flow control portion that is connected to the furnace for controlling the flow of the atmospheric gas, a gas generator for producing an endothermic gas (Rx gas) and supplying the flow control portion with the endothermic gas, and a gas analyzing control portion for analyzing the atmospheric gas that is supplied through a sampling line that is connected to the furnace and for controlling the flow control portion based on the analyzed data so as to control a flux of the atmospheric gas that is supplied to the furnace. With the system, decarbonization of carbon steel can be prevented or reduced.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2008-0031733 filed on Apr. 4, 2008, the entirecontents of which are incorporated herein by reference.

BACKGROUND

(a) Technical Field

The present disclosure relates to a furnace for treating carbon steelwith heat, and more particularly to a system for controlling atmosphericgas that is supplied into the furnace.

(b) Background Art

When oxygen flows into a heat treatment furnace or oxygen is generatedtherein, the oxygen reacts with the carbon steel in the furnace todecarbonize the carbon steel. The decarbonization lowers the dimensionalprecision of the steel product.

The decarbonization is a phenomenon in which carbon steel reacts withoxygen at a high temperature and the carbon of the carbon steel isremoved as CO or CO₂ so that the carbon concentration of the steelsurface is reduced, thereby transforming the carbon steel to a softferrite material.

The decarbonization may lower the hardness of the steel product. It alsomay generate tensile stress in a surface portion of the carbon steel,causing a deformation thereof or a crack therein. One method to reducethe decarbonization is to supply the heat treatment furnace with anatmospheric gas such as nitrogen and an endothermic gas.

However, when the contents of outside air, oxygen, carbon dioxide,vapor, or sulfur dioxide is higher than that in an equilibrium conditionwithin the furnace while the atmospheric gas is supplied to the furnace,decarbonization occurs therein.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the invention andtherefore it may contain information that does not form the prior artthat is already known in this country to a person of ordinary skill inthe art.

SUMMARY

The present invention has been made in an effort to provide a system forcontrolling atmospheric gas inside a furnace having advantages ofpreventing decarbonization of carbon steel that is treated with heat inthe furnace.

A system for controlling atmospheric gas inside a furnace may include afurnace for treating carbon steel with heat at a predeterminedtemperature and into which an atmospheric gas is charged, a flow controlportion that is connected to the furnace for controlling the flow of theatmospheric gas that is supplied to the furnace, a gas generator forproducing an endothermic gas (Rx gas) and supplying the flow controlportion with the endothermic gas, and a gas analyzing control portionthat analyzes the atmospheric gas that is supplied through a samplingline that is connected to the furnace and that controls the flow controlportion based on the analyzed data so as to control a flux of theatmospheric gas that is supplied to the furnace.

The flow control portion may include a first supply line through whichnitrogen gas passes and a second supply line through which theendothermic gas passes, and a solenoid valve or a control valve that iscontrolled by the gas analyzing control portion is disposed on the firstsupply line and the second supply line.

The first supply line may include a solenoid valve that is opened duringa power failure, and a control valve that is PID-controlled according toa PF value that is analyzed in the gas analyzer.

The gas generator may use LNG to produce the endothermic gas, the gasanalyzing control portion analyzes the CO2 amount of the endothermicgas, and the gas analyzing control portion determines whether the CO2amount is in a predetermined range.

The gas analyzing control portion may include a gas sensor for analyzingcarbon monoxide, carbon dioxide, or oxygen, a PF calculator thatcalculates a PF value based on signals that are detected by the gassensor, and a control portion that compares the calculated PF value witha predetermined PF value so as to control the control valve of the flowcontrol portion.

The gas analyzing control portion may analyze contents of theendothermic gas that is produced in the gas generator to determine theperformance of the gas generator.

The atmospheric gas within the furnace is sampled to be analyzed, andthe inflow amount of the atmospheric gas that is supplied into thefurnace is controlled based on the analyzed data so as to reduce thedecarbonization according to the system for controlling atmospheric gasinside the furnace of an exemplary embodiment of the present invention.

The above and other features will be discussed infra.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a system for controlling an atmosphericgas inside a spheroidizing heat treatment furnace according to anexemplary embodiment of the present invention.

FIG. 2 is a schematic diagram of a gas generator according to anexemplary embodiment of the present invention.

FIG. 3 is a control flow chart of an a system for controlling anatmospheric gas inside a spheroidizing heat treatment furnace accordingto an exemplary embodiment of the present invention.

DESCRIPTION OF REFERENCE NUMERALS INDICATING PRIMARY ELEMENTS IN THEDRAWINGS

-   -   100: flow control portion    -   102: fire check valve    -   104, 112, 116: solenoid valve    -   114, 106: control valve    -   118, 119: flow meter    -   120: gas analyzing control portion    -   122: heater    -   130: gas generator    -   200: LNG flow meter    -   202: filter    -   204: air flow meter    -   206: blower    -   208: retort    -   210: cooler    -   300: chamber (furnace)    -   302: gas analyzer    -   304: AC/DC converter    -   306: PF calculator    -   308: PI calculator    -   310: controller    -   312: throttle position controller    -   314: valve controller    -   316, 318: control motor

DETAILED DESCRIPTION

The present invention will be described more fully hereinafter withreference to the accompanying drawings, in which exemplary embodimentsof the invention are shown. As those skilled in the art would realize,the described embodiments may be modified in various different ways, allwithout departing from the spirit or scope of the present invention.

FIG. 1 is a schematic diagram of a system for controlling an atmosphericgas inside a spheroidizing heat treatment furnace according to anexemplary embodiment of the present invention.

Referring to FIG. 1, the atmospheric gas control system includes afurnace 110, a flow control portion 100, a gas analyzing control portion120, and a gas generator 130.

The inside of the furnace 110 is heated to a predetermined temperature(about 770° C.) so as to heat-treat the carbon steel therein, and theinside thereof is filled with an atmospheric gas so as to reducedecarbonization of the carbon steel.

A supply line is suitably disposed to supply the atmospheric gas intothe furnace 110, and a sampling line is suitably disposed to exhaust theatmospheric gas to the outside of the furnace 110.

Preferably, the flow control portion 100 includes a first supply linefor supplying nitrogen gas and a second supply line for supplying anendothermic gas.

Flow meters 118 and 119 may suitably be disposed on the first supplyline and the second supply line, respectively. The flow meters 118 and119 are used to precisely control the gas that is supplied and generatean alarm signal when there is a power failure. Also, solenoid valves112, 116, and 104 and control valves 114 and 106 may suitably bedisposed in the first supply line and the second supply line,respectively.

The solenoid valve 116 is closed in a normal condition and may be openedwhen the electricity is off. The solenoid valve 112 is open.Accordingly, the atmospheric gas is securely supplied into the furnace110. Also, the opening rate of the control valve 114 is properlycontrolled in a range from 0 to 100% according to the content amount ofthe atmospheric gas within the furnace 110.

The gas generator 130 may produce endothermic gas, and the producedendothermic gas is supplied into the furnace 110 through the secondsupply line of the flow control portion 100.

The opening rate of the control valve 106 is adequately controlled in arange from 0 to 100% according to the state of the atmospheric gaswithin the furnace 110.

The atmospheric gas is supplied to the gas analyzing control portion 120via the sampling line that is connected to the furnace 110 through aheater 122. A fire check valve 102 may suitably be disposed on a linebetween the flow control portion 100 and the gas generator.

The gas analyzing control portion 120 analyzes the supplied atmosphericgas. According to an embodiment, the gas analyzing control portion 120analyzes the content amounts of carbon dioxide, carbon monoxide, andoxygen, and controls the flow control portion 100 based on theinformation about the content amounts.

Also, the gas analyzing control portion 120 receives the endothermic gas(Rx gas) that is produced from the gas generator 130 and analyzes theamount of the carbon dioxide that is included in the endothermic gas.

The gas analyzing control portion 120 analyzes the contents of theatmospheric gas to effectively control the opening rates of the controlvalves 114 and 106 and the solenoid valves 112, 116, and 104 of the flowcontrol portion 100 based on the information about the analyzedcontents.

Preferably, the gas analyzing control portion 120 may calculate a PFvalue and PID-control (Proportional Integral Differential control) thevalves (112, 114, 116, 106, and 104) to effectively supply theatmospheric gas into the furnace and reduce decarbonization.

The gas analyzing control portion 120 analyzes the content of the carbondioxide that is included in the endothermic gas to detect theperformance of the gas generator 130.

Fire check valves (F) may suitably be disposed between the gas generator130 and the flow control portion 100 and between the furnace 110 and thegas analyzing control portion 120.

FIG. 2 is a schematic diagram of a gas generator according to anexemplary embodiment of the present invention.

The gas generator 130 mixes LNG with air in a proper ratio to producethe endothermic gas (Rx gas). The gas generator 130 may suitably includean LNG flow meter 200 for detecting a flux of the LNG, an air filter202, an air flow meter 204, a blower 206, a retort 208, and a cooler210. A detailed description of the gas generator 130 will be omitted inthe present exemplary embodiment.

A portion of the endothermic gas that is generated from the gasgenerator 130 is analyzed in the gas analyzing control portion 120 todetect the performance of the gas generator 130.

FIG. 3 is a control flow chart of a system for controlling anatmospheric gas inside a spheroidizing heat treatment furnace accordingto an exemplary embodiment of the present invention.

Referring to FIG. 3, the gas control system that is installed in achamber 300 of the furnace, suitably, includes a gas analyzer 302, anAC/DC converter 304, a PF calculator 306, a PI (Proportional Integral)calculator 308, a controller 310, a throttle position controller 312, avalve controller 314, and control motors 316 and 318.

The constituents of the atmospheric gas sample that is supplied from thechamber 300 of the furnace are analyzed in the gas analyzer 302. Also,the gas analyzer 302 outputs a DC current according to the conditions ofthe analyzed gas.

The AC/DC converter 304 transforms to an AC current the DC current thatis outputted from the gas analyzer 302. The gas analyzer 302 maypreferably include a carbon dioxide sensor, a carbon monoxide sensor,and an oxygen sensor.

The PF calculator 306 calculates a PF value based on the current valuethat is transferred from the AC/DC converter 304. Also, the PIcalculator 308 compares the PF value that is transferred from the PFcalculator 306 with a predetermined PF value of the controller 310 tocalculate a PI value.

The throttle position controller 312 transmits an operation current tothe valve controller 314 according to the PI value that is transferredfrom the PI calculator 308.

The valve controller 314 operates the control motors 316 and 318according to the operation current that is transferred from the throttleposition controller 312.

Accordingly, the control motor 316 that is disposed in the endothermicgas supply line and the control motor 318 that is disposed in thenitrogen supply line are adequately controlled based on the contents ofthe atmospheric gas of the chamber 300 in the control process that isstated above.

Referring to FIG. 1 and FIG. 3, suitably, the gas analyzing controlportion 120 controls the carbon dioxide to be in a range of 0 to 5%, andcontrols the carbon monoxide to be in a range of 0 to 25% among theatmospheric gas within the furnace 110. Also, the gas analyzing controlportion 120 controls the oxygen to be in a range of 0 to 25%.

For example, when the carbon dioxide or the oxygen value is raised, thesupply amount of the nitrogen or the endothermic gas is raised to reducethe decarbonization reaction.

Preferably, the PF value that is calculated in the PF calculator 306 iscontrolled to be in a range of 0 to 250 or 0 to 500. Also preferably,the gas analyzing control portion 120 analyzes the content of the carbondioxide that is included in the endothermic gas produced in the gasgenerator 130 to determine the performance of the gas generator 130 andto control production amount.

With regard to the PF value, for example, carburization occurs in somedegrees when the PF value is larger than 65 and decarbonization occurswhen the PF value is lower than 65. Generally, as the temperaturebecomes higher, the PF value also becomes higher.

While this invention has been described in connection with what ispresently considered to be practical-exemplary embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1. A system for controlling atmospheric gas inside a furnace,comprising: a furnace into which an atmospheric gas is charged fortreating carbon steel with heat at a predetermined temperature; a flowcontrol portion that is connected to the furnace for controlling theflow of the atmospheric gas that is supplied to the furnace; a gasgenerator for producing an endothermic gas (Rx gas) and supplying theflow control portion with the endothermic gas; and a gas analyzingcontrol portion that analyzes the atmospheric gas that is suppliedthrough a sampling line that is connected to the furnace and thatcontrols the flow control portion based on the analyzed data so as tocontrol a flux of the atmospheric gas that is supplied to the furnace.2. The system for controlling atmospheric gas of claim 1, wherein theflow control portion comprises: a first supply line through whichnitrogen gas passes; a second supply line through which the endothermicgas passes; and a solenoid valve or a control valve that is controlledby the gas analyzing control portion and that is disposed on the firstsupply line and the second supply line.
 3. The system for controllingatmospheric gas of claim 2, wherein the first supply line comprises: asolenoid valve that is opened during a power failure; and a controlvalve that is PID-controlled according to a PF value that is analyzed inthe gas analyzer.
 4. The system for controlling atmospheric gas of claim1, wherein the gas generator uses LNG to produce the endothermic gas,the gas analyzing control portion analyzes the CO₂ amount of theendothermic gas, and the gas analyzing control portion determineswhether the CO₂ amount is in a predetermined range.
 5. The system forcontrolling atmospheric gas of claim 1, wherein the gas analyzingcontrol portion comprises: a gas sensor for analyzing carbon monoxide,carbon dioxide, and oxygen; a PF calculator that is used to calculate aPF value based on signals that are detected by the gas sensor; and acontrol portion that compares the calculated PF value with apredetermined PF value so as to control the control valve of the flowcontrol portion.
 6. The system for controlling atmospheric gas of claim1, wherein the gas analyzing control portion analyzes contents of theendothermic gas that is produced in the gas generator to determine theperformance of the gas generator.